Preparation of tetraalkyllead



Patented Dec. 26, 1950 2,535,236 PREPARATIdN OF TETRAALKYLLEAD Hymin Shapiro, Detroit, Mich., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application May 29,1948,

Serial No. 30,192

4 Claims. (Cl. 260-437) This invention relates to the manufacture of tetraalkyllead. More particularly, it relates to a process for reacting a magnesium-lead alloy with an alkyl chloride in the presence of selected catalysts to form a tetraalkyllead.

The manufacture of tetraethyllead is of considerable importance because of its use as an antiknock agent in motor fuels. It is used in most of the gasolines presently marketed. Therefore, the economics of its manufacture is also of major importance.

The present commercial process for the manufacture of tetraethyllead has been used for a number of years, and, in general. is satisfactory. However, it has certain disadvantages which are overcome by practicing my invention. The present commercial process is expressed by the following chemical equation:

In the process as illustrated in the above equation, if the composition of the alloy is controlled to correspond substantially to NaPb, the reaction goes readily to completion without a catalyst and tetraethyllead yields of about 21 per cent by weight based on the lead input are obtained.

It is to be noted, however, that in the NaPb reaction, less than one-quarter of the lead originally present in the alloy is converted to tetraethyllead. The remaining three-quarters of the original lead present is converted to finely divided metal considerably contaminated with the product. The presence of this large amount of unused lead in the autoclaves makes temperature control difllcult, results in a low overall rate of product output, and necessitates a relatively large investment in equipment as compared with the more efllcient processing of the lead obtainable in practicing my invention. Furthermore, the conversion of the finely divided lead to a form suitable for use in making thfaPb alloy is a hazardous and expensive operaion.

It is an object of this invention to provide a process for making tetraalkyllead overcoming the above objections, particularly in making more emcient use of the lead. This is accomplished in my invention by reacting a magnesium-lead alloy with an alkyl chloride in the presence of selected catalysts as illustrated by the following chemical equation:

Temp.

2 It is to be noted that in the above equation, no load in the alloy is converted to metallic lead as contrasted with over '75 per cent lead converted from the alloyto finely divided metal in the present commercial operations.

The above reaction is carried out in the presence of a catalyst. While neither the exact mechanism of the reaction nor the effect of catalyst structure on the reaction is known, I have found that a catalyst comprising a mixture of an organic compound containing an atom capable of chemical coordination with a magnesium-containing compound, and an alkyl iodide are the most effective for economically producing high yields of tetraalkyllead compounds. Among the organic catalysts having such properties are aliphatic ethers and tertiary amines, including aliphatic and aromatic tertiary amines, in which the coordinating atom is either oxygen or nitrogen.

The catalysts that I have found to be most effective are an alkyl iodide, such as the iodides of methane, ethane, propane, butane, and pentane, mixed with one or more of the following: aliphatic ethers and tertiary amines, including tertiary aliphatic amines, tertiary aromatic amines, and tertiary aliphatic-aromatic amines. Examples of aliphatic ethers are methyl ether, ethyl ether, propyl ether, and isobtuyl ether. Illustrative of tertiary amines that can be used are triethyl amine, tripropyl amine, tributyl amine, triphenyl amine, methyl diphenyl amine, and dimethyl phenyl amine.

Various alkyl chlorides can be used to react with the MgzPb alloy to form the corresponding tetraalkyllead compounds, such as the chlorides of methane, ethane, propane, butane, and pentane.

My process can be carried out at temperatures up to 150 degrees centigrade, although the preferred range is to degrees centigrade.

Pressures from a few pounds above atmospheric to several hundred pounds per square inch can be employed advantageously. Best yields are obtained by using an alloy corresponding to Mg'sPb (19.01 per cent Mg by weight), but good yields are obtainable with a magnesium content varying from 18 to 22 per cent by weight. As the magnesium content varies outside of this range inferior results are obtained, and furthermore, the alloy is more diflicult to crush preparatory to using.

The time for the reaction can also be varied over a wide range. In closed bomb operations, the reaction time has been varied between two wide limits, 1. e., between one and 13.0 per cent by weight of the alloy charged has been used. The proportion and type of catalyst used and the operating conditions of temperature, pressure and time will vary in order for optimum results to be obtained, and need to be correlated with the alkyl chloride used to obtain the highest yield of tetraalkyllead compounds.

My invention is further illustrated by the following example: 10 grams of MgzPb alloy, 20 grams of ethyl chloride, and a catalyst comprising one gram of ethyl iodide and V2 gram of ethyl ether are introduced into a tumbled bomb. The alloy, comprising about 19 per cent by weight magnesium, was first ground in a "chipmunk" crusher to a particular size, varying from 4 to 100 mesh, substantially three-quarters of the ground alloy being in the range of 4 to 40 mesh. The ethyl chloride, the ethyl iodide and the ethyl ether are ordinary commercial grades. The material was charged into the bomb preferably in the order: alloy, ethyl chloride, and catalyst. tumbled for four hours at 100 degrees centigrade. The reaction is exothermic and cooling must be employed after the reaction is unde way in order to maintain the desired temperature. In this experiment, the temperature was controlled by controlling the temperature of the bath in which the bomb was immersed. In commercial practice, cooling water suitably applied can be used.

The bomb was then closed oi! and cent by weightmagnesium) and 20 grams of ethyl chloride were used. The table summarizes results obtained using diil'erent operating conditions and difierent catalysts, with yields varying between 68 and 8'1 per cent by weight based on the lead input. j v

In all cases the 20 grams oi ethyl chloride represents twice the amount'oi ethyl chloride required to react with all the lead contained in the alloy. In other words, twice the stoichiometric equivalent of ethyl chloride was used in all the examples, although this can be varied over wide limits as long as an excess of ethyl chloride is used.

Referrlngto the table, Column '1 gives the example number; Columns 2, 3, and 4 refer to the conditions of operation; Column 2, to the length of time the reactants remained in the bomb; Column 3, to the temperature maintained during the reaction, and Column 4, to the pressure in poundsper square inch. The pressure indicated is the pressure which resulted from the materials charged at the temperature under which the bomb was maintained. Again referring to the table, Columns 5, 6, andv 7 refer to the catalyst used; Column 5 to the name of the catalyst; Column 6, to the grams charged, and Column 7, to the per cent by weight of catalyst based on alloy charged. Columns 8 and 9 relate to the tetraalkyl product, Column 8 referring to the grams recovered, and Column 9, to the percentage yield based on the lead in the alloy charged.

Summary of experiments Conditions Catalyst Yield Exlazmple Time, Temp. PremneLbs. Per Per Hours C. pa-Sqln. Name cent Grams Grams cont Fth lloriide 10 1.0 1 4 100 139 {Etglmheruu 5 M 8.62 63.2

Ethyl Iodide. 3.0 2 2 120 196 gtgyllEtdhsiru 5 0.5}

t y o i e. 85 8.5 a 2 100 123 5 0'5 11.0 87.0

. y 0 e. 85 8.5 4 2 120 ;g)r0lI)y(11theL 69.2 6.92} 0 i e. 85 8.5 5 2 120 m1 ia gg gvfi M 10.3 81.1

e y o e 6.5 l 6 2 120 196 Ethyl Ether 10 L0 I 8.22 0.1.0

Fthyl Iodide 20 2.0 I 7 4 120 201 thyl Fthil' 5 0.51 10.8 85.3

'lriethyl A mine 5 0 Fthyl Iodide 10 l. 0 8 4 136 TthylFth 5 0.5 10.4 82.1

Dimcthylphenylamin 6 O. 6 Ethyl Iodld 20 2.0 9 2 100 134 Ethyl Ether 5 0.5 10.9 86.0

Dimethylpheuylamine 6 6. 0 Ethyl Iodide 10 1.0 10 4 100 139 Fthyl Ether 5 0.5 8.84 69.9

Pyridine 3. 9 0. 39

At the end of four hours, the bomb is cooled and the product analyzed for tetraethyllead. In commercial practice, the product may be distilled and vacuumed in the presence of steam to recover the tetraalkyllead product. In this example, analysis showed that 8.62 grams of tetraethyllead were produced, which is equivalent to 68.2 per cent by weight based on the lead input, as compared with the 21.0 per cent obtained in present commercial operations using NaPb alloy.

The results of the above experiment are tabulated as Example No. 1 in the table given below entitled Summary of Experiments. The results of nine additional experiments conducted in a similar manner are also tabulated. In all the examples, 10 grams of MgzPb alloy (19 per n In all the examples, ethyl iodide was used as a catalyst. In Examples 1 to 6, inclusive, binary catalysts were used; in Examples '7 to 10, inclusive, ternary catalysts were used. It should be noted that, in general, other conditions being equal, the yield increased with use of a ternary catalyst.

In all cases, an excess of alkyl chloride over the theoretical amount required is used and preferred. Not only does an excess increase the yield, but it also increases the. rate of production, which is important in commercial operation because it reduces equipment size and cost. Also, an excess of alkyl chloride maintains a liquid which provides for better heat transfer in maintaining, by cooling, the desired temperature of operation.

Although the alkyl iodide has been referred to herein as a catalyst, it is in reality a promoter for the catalysts. Insignificant yields result when neither a catalyst nor a promoter is used. When the alkyl iodide promoter is used alone in the reaction, i. e. no catalyst used, inferior results are obtained. .When either alykyl ethers or tertiary amines, either singly or combination are used, i. e. as catalysts, yields of lead alkyls of the order of about 50% are obtained. However, when an alkyl iodide is present with the catalysts, a promoter effect is obtained and the yield due to the promoter is increased from about 50% to about 80 definitely demonstrating the improved results obtained with the alkyl iodide promoter.

The examples given herein are illustrative of my invention, but do not limit the scope of my invention. The reaction can be carried out in batch or continuous operations. The manner of operation, as well as the equipment used can be considerably varied within the scope of my invention.

I claim:

1. In the process for making tetraalkyllead by reacting a lower alkyl chloride with an alloy consisting of lead and magnesium in the presence of an alkylating catalyst containing an atom which chemically coordinates with magnesium, the step comprising conducting said reaction in the presence of a lower alkyl iodide.

2. In the process for making tetraalkyllead by reacting a lower alkyl chloride with an alloy consisting of lead and magnesium in the presence of an aikylating catalyst containing an atom which chemically coordinates with magnesium, the step comprising conducting said reaction in the presence of ethyl iodide.

3. A process for making tetraalkyllead comprising reacting a lower alkyl chloride with an alloy consisting of about 18 to 22 percent by weight magnesium and about 78 to 82 percent by weight lead, in the presence of a lower alkyl iodide and a catalyst selected from the group consisting of aliphatic hydrocarbyl ethers and tertiary hydrocarbyl amines.

4. A process for making tetraethyllead comprising reacting ethyl chloride with an alloy consisting of about 19 percent by weight magnesium and about 81 per cent by weight lead in thepresence of ethyl iodide and diethyl ether.

HYMIN SHAPIRO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,000,069 Downing et a1. May 7, 1935 OTHER REFERENCES Calingaert: Chemical Reviews," vol. 2 (1925), pp. 46-48. 

1. IN THE PROCESS FOR MAKING TETRAALKYLLEAD BY REACTING A LOWER ALKYL CHLORIDE WITH AN ALLOY CONSISTING OF LEAD AND MAGNESIUM IN THE PRESENCE OF AN ALKYLATING CATALYST CONTAINING AN ATOM WHICH CHEMICALLY COORDINATES WITH MAGNESIUM THE STEP COMPRISING CONDUCTING SAID REACTION IN THE PRESENCE OF A LOWER ALKYL IODIDE. 